Treating tank for thermoplastic materials and the like



Jan. 22, 1957 H. E. BIRKNER, JR 2,778,922

TREATING TANK FOR THERMOPLASTIC MATERIALS AND THE LIKE Filed Aug. 27, 1953 2 Sheets-Sheet l 1N VEN TOR. #040 1 fimK/vne J78 Jan. 22, 1957 H. E. BIRKNER, JR 2,778,922

TREATING TANK FOR THERMOPLASTIC MATERIALS AND THE LIKE Filed Aug. 27, 1953 2 Sh eets-Shee'i: 2

4 INVENTOR. #040 L Emzucg J22 BY 1622, 7} 0mm TRIKE/l United States Patent TREATING TANK FOR THERMOPLASTIC MATERIALS AND THE LIKE Hugo E. Birkner, Jr., Kent, Ohio, assignor to Sta-Warm Electric Co., Ravenna, Ohio, a corporation of Ohio Application August 27, 1953, Serial No. 37 6,936

4 Claims. (Cl. 219-44) This invention relates to improvements in or relating to a treating tank for thermoplastic materials or the like and particularly improvements in or relating to a heated agitator equipped tank for melting thermoplastic and other similar materials. These therefore are the general objects of the present invention.

A more specific object of the present invention is the provision of an improved electrically heated melting tank for rendering thermoplastic material plastic and for retaining such material in a plastic condition in an economical and high efiicient manner.

Other objects and advantages of the present invention will become more apparent from the following description of a practical embodiment of the invention which is illustrated in the accompanying drawings. The essential features of the invention will be summarized in the claims.

In the drawings, Fig. 1 is an elevation of an improved electrically heated agitator equipped plastic melting tank constructed in accordance with the present invention;

Fig. 2 is a vertical section of the improved tank with the agitator drive mechanism and its support omitted, the plane of the section being indicated by the line 22 on Fig. 1;

Fig. 3 is an elevation of the agitator removed from the tank;

Fig. 4 is a top view of the agitator; and

Fig. 5 is an electrical diagram illustrating the electric heating elements and their associated controls.

Referring now to the drawings in detail, and particularly to Figs. 1 and 2, it will be seen that the improved melting tank includes an open top cylinder within which a second cylinder is positioned. Both cylinders are formed of sheet metal and their axes are coextensive. The external diameter of the inner cylinder is less than the internal diameter of the outer cylinder to provide an annular spac to receive the material to be treated. This space is closed at its bottom by an annular bottom wall 11, and the inner cylinder is closed at its top by a top wall 19, which is spaced a short distance below the top of the cylinder 10.

Electric heating elements generally indicated at are applied directly to and encircle the outer wall of the outer cylinder 10. These elements extend from a point adjacent the top of such wall downwardly around the bottom wall 11 and thence upwardly along the inner wall of the inner cylinder 15.

The bottom wall 11 is provided with a discharge opening 12 to which a valve 14 is connected. The valve is provided with a manually operable handle 15 and is heated by heating elements 26 which are wrapped about the valve.

The heating elements which are protected by the usual insulation material are applied directly to the walls of the cylinders and the valve. A layer of heat insulating material 17 surrounds the cylinder 10 and valve 14. This layer extends throughout substantially the entire length of the cylinder 10 and entirely across the bottom of both cylinders and provides a closure for the space 18 within the inner cylinder 15. The space 30 serves as a heat storage space, and preferably has a volume which is from one-fifth to one-tenth the volume of the annular space 20. Such relationship has been found to maintain the contents of the annular space 20 in a plastic condition with a minimum consumption of electrical energy and thus provides a highly economical and efiicient structure.

The insulating material 17 is held in place by an outer metal jacket 21 which tightly surrounds the insulation and which is closed at its bottom as indicated at 22. If desired the outer jacket 21 may be spaced from the container 10 by suitable spacing members, one of which is indicated in Fig. 2 at 23.

The material to be melted or rendered plastic is placed in the container in chunks and, when molten is agitated by an agitator 30 to maintain the same consistency and temperature throughout the area of the space 20. This agitator is supported by a shaft 31 the lower end of which seats in a bearing 32 carried by the top 19 of the inner cylinder 15. The upper end of this shaft is supported by a drive unit 35. As shown the shaft 31 is connected by a coupling 36 with a reduction gear unit 37 of the drive unit 35. The drive unit is carried by a platform 40 which is secured to the outer jacket 21 of the container by suitable brackets 41. The reduction gear unit 37 is drivingly connected with an electric motor 38 also supported by the platform 40. If desired a cover 45 may be provided through which the agitator shaft extends. This cover may be provided with lugs 48 which may be clamped to similar lugs 4 of the container 10 to retain the cover in position. The arrangement is such that the cover may be raised above the container 10 to permit charging of the container.

A preferred form of agitator is shown in Figs. 3 and 4. As there shown a plurality of arms 50 extend outwardly from the base of the shaft 31 and are connected with downwardly extending spiraled blades 51, the lower ends of which are connected to an annulus 52 as by welding. The blades 51 spiral in a counterclockwise direction for purposes hereinafter to be more fully explained. The annulus 52 is slightly larger than the diameter of the cylinder 15 and is positioned closely adjacent the bottom thereon. The arrangement is such that the blades 51 will rotate in proximity to the outer Wall of the cylinder 15. Extending outwardly from the arms 50 are other arms 55. Similar arms 56 are secured to and extend outwardly from the annulus 52 adjacent the bottom of the container 10. A series of relatively narrow blades 57 extend downward from the arms 55 to respective arms 56. These blades are spiraled in a clockwise direction for purposes hereinafter to be explained. These blades 57 lie closely adjacent the inner wall of the cylinder 10 and may be secured intermediate their ends to the blades 51 by relatively narrow webs 58. The arrangement of the blades 51 and 57 is such that there is approximately one eighth of an inch clearance between the outer edge of the blades and the adjacent cylinder wall.

When the agitator drive is such that it rotates the agitator shaft 31 in a clockwise direction, the outer blades 57 which spiral in a clockwise direction tend to force the contents of the tank downwardly along the wall of the cylinder 10, while the blades 51 which spiral in a counterclockwise direction then tend to draw the contents upwardly along the outer wall of the cylinder 15. Thus the contents of the container is forced to circulate generally as indicated by the arrows 59 in Fig. 2. The reverse would be true were the agitator driven in a counterclockwise direction.

It will be noted that the agitator illustrated is provided with two outer blades 57 which have a relatively gradual spiral and four inner blades 51, the spirals of which are relatively steep. As shown the outer blades spiral substantially over an angle of 180 whereas the inner blades are spiraled for substantially an angle of 90". This arrangement tends to move the material along the wall of the inner cylinder at a more rapid rate than the material is moved in the reverse direction along the wall of the outer cylinder. T his eliminates undesired turbulence and frothing of the material being agitated. Further it causes the volume of material flowing along the relatively large surface of the cylinder 10 to flow the opposite direction along the relatively small area of the cylinder 15 without ereating undue pressures at either the top or bottom or the container. Likewise the improved agitator permits the entire mass of fluid or plastic in the space 20 to be agitated with comparatively narrow blades, thus reducing to a minimum the power required to drive the agitator.

Fig. 5 illustrates a preferred manner of controlling the electric heating elements. The heating elements of the inner and outer cylinders are electrically divided substantially at the horizontal mid-point of the container as indicated in Figs. 2 and 5 by the dotted line 60, thus providing elements 61 for the upper portion of the cylinders 10 and 15, a d elements 62 for the lower portion of the cylinders 10 and 15, the bottom wall 11 and the valve 14. These elements are connected with a source of electrical energy by conductors 64 and 65. The conductor 64 is connected with one pole of a switch 66 which is controlled by a thermostat 67 positioned within the tank and adjacent the bottom thereof. The other pole of the switch 66 is connected by a conductor 68 with one pole of the elements 61 and 62. The other pole of each element 61 and 62 is connected with one pole of a respective thermal switch 71 which are responsive to the temperature of the wall of the outer container 10. The other poles of these switches are connected with the conductor 65. Accordingly both heating elements 60 and 61 are energized and deenergized in response to the temperature of the contents of the tank adjacent to the bottom wall thereof. However, the contents of the upper and lower portions of the tank are also individually responsive to their temperature of the respective wall portions of the container 10. One advantage of this arrangement is that the heat applied to. the upper portion of the tank is automatically cut as the level of the contents drops due to withdrawal of the material from the tank. Thus overheating the tank is prevented. While I have illustrated two control sections it is obvious that the number of the control sections may be increased, for instance, the tank may be divided in thirds vertically, all three sections being under the common control of the thermostat 67', and each section being individually controlled by its respective thermostat 71. This not only avoids overheating of the contents of the tank but assists materially in reducing the amount of electrical energy required to maintain the contents molten as it avoids loss ofheat.

I claim:

1. A tank for treating thermoplastic materials and the like comprising a pair of vertically extending cylinders positioned one within the other with their axes coextensive, the inner cylinder having a diameter materially smaller than the diameter of the outer cylinders to provide an annular material receiving space between the two cylinders, closure means for the bottom of said space, means to heat the outer walls of said cylinders, an agitator disposed within the space between the two cylinders, said agitator comprising a plurality of relatively narrow blades spiraled vertically adjacent the inner wall of the outer cylinder and a plurality of relatively narrow blades spiraled vertically about the outer wall of the inner cylinder, one set of blades being spiraled clockwise and the other set of blades being spiraled counter-clockwise, and means to rotate said agitator.

2. A material treating tank for thermoplastic materials according to claim 1 wherein the blades positioned adjacent the wall of the inner cylinder are more steeply spiraled than the blades adjacent the wall of the outer cylinder whereby the rotation of the agitator will cause the material in the tank to flow upwardly along the wall of the inner cylinder at a greater rate of speed than the rate at which the material flows downwardly along the wall of the outer cylinder.

3. A tank for treating thermoplastic materials and the like comprising a pair of vertically extending cylinders positioned one within the other with their axes coextensive the inner cylinder having a diameter materially smaller than the diameter of the outer cylinders to provide an annular material receiving space between the two cylinders, closure means for the bottom of said space, means to heat, the outer walls of said cylinders, an agitator disposed within the space between the two cylinders having an agitator provided with one set of blades to cause the fluid or plastic material to flow downward along the wall of the outer cylinder and a second set of blades to cause the material to flow upwardly along the wall of the inner cylinder.

4. A material treating tank for thermoplastic materials or the like according to claim 3 wherein said agitator blades are shaped relating to each other to cause the material in the tank to flow upwardly along the wall of the inner cylinder at a greater rate of speed than the material flows downwardly along the wall of the outer cylinder.

References Cited in the file of this patent UNITED STATES PATENTS 

